function[I2]=jpeg(nomfich,q_jpeg)
    if q_jpeg >= 1 && q_jpeg <= 50
        alpha = 50/q_jpeg;
    elseif q_jpeg >= 50 && q_jpeg <= 99
        alpha = 2-(2*q_jpeg/100);
    end


    Q=[16 11 10 16 24 40 51 61;
       12 12 14 19 26 58 60 55;
       14 13 16 24 40 57 69 56;
       14 17 22 29 51 87 80 62;
       18 22 37 56 68 109 103 77;
       24 35 55 64 81 104 113 92;
       49 64 78 87 103 121 120 101;
       72 92 95 98 112 100 103 99];


    A=imread(nomfich);
    I=double(A)-128;

    Q = alpha*Q;

    B=blkproc(I,[8 8],'dct2(x)'); 
    B1=fix(blkproc(B,[8 8],'x./P1',Q));
    B2=fix(blkproc(B1,[8 8],'x.*P1',Q));
    
    I2=blkproc(B2,[8 8],'idct2(x)');
    
    I2=uint8(128+I2);
    %imshow(A),figure,imshow(I2);

   
    